Radio communication spectrums are precious natural resources, and the scarcity of the spectrum resources has been increasingly serious along with rapid development of wireless communication technologies. As adopted in wireless communication networks, spectrums are fixedly allocated at present, resulting in that spectrum resources allocated to some system heavily loaded with traffic are not sufficient while spectrum resources occupied by some system lightly loaded with traffic are excessive, thus failing to efficiently use the fixedly allocated spectrum resources. The technology of Cognitive Radio (CR) has emerged in response to a need to improve the utilization ratio of the spectrum resources.
A principle of the technology of cognitive radio lies in that: given no interference to an authorized system, a change in current radio communication environment is detected intelligently to select dynamically a blank frequency of the authorized system for communication so as to address the existing problem of unreasonable utilization of the spectrum resources due to fixed allocation of the spectrums. The blank frequency refers to an idle frequency allocated to the authorized system. With the technology of cognitive radio, an access system, capable of communication using an idle radio communication spectrum allocated to the authorized system, is referred to a cognitive system.
A blank frequency may be discovered and used by a plurality of cognitive systems, so in a currently common mechanism, a cognitive system at a low priority concedes actively to a cognitive system at a high priority, that is, when the cognitive system at a high priority communicates at some blank frequency, the cognitive system at a low priority can use the blank frequency when the blank frequency is out of use by the cognitive system at a high priority, or the cognitive system at a low priority may concede from the spectrum resource when the cognitive system at a high priority needs to use the spectrum resource. As can be apparent, the blank frequency typically varies dynamically, and an operating frequency of the cognitive system may also vary therewith, thereby an access system at a frequency also varies dynamically.
A terminal needs to search for a cell after being powered on, and if prior information is stored in the terminal (the prior information includes at least information about a frequency previously used by the terminal), then the terminal searches for a cell preferentially at the frequency in the prior information, and if there is an appropriate cell detected, then the terminal may select and reside at the cell; and if there are a plurality of frequencies in the prior information, then the terminal may firstly measure power at the frequencies and then perform operations, such as downlink synchronization and read of information over a broadcast channel, preferentially at the frequency with maximum power. However the frequency used by an access system is dynamically variable, and the access system at a frequency also varies dynamically, thus the frequency or frequencies in the prior information stored in the terminal may not necessarily be a frequency or frequencies available for a network accessed by the terminal, and if not, the terminal might waste considerable time on unnecessary downlink synchronization and other operations, thus prolonging a delay in cell selection and cell residence. If there is no prior information in the terminal, then the terminal may make a blind search throughout a frequency band in its supported bandwidth until an appropriate cell is detected, thus resulting in a delay in cell selection and cell residence.
In a CR system, the access system at the frequency also varies dynamically, and if the terminal scans the power at the frequencies based on the stored prior information, but the scanned frequency with maximum power might not necessarily be a frequency available for a network accessed by the terminal, then the terminal might waste considerable time on unnecessary downlink synchronization and other operations, thus prolonging a delay in cell selection and cell residence and decreasing the user experience.
In summary, when the terminal searches for a cell in the existing CR system, the frequency used by the access system is dynamically variable, so that the terminal may tend to waste considerable time on unnecessary downlink synchronization and other operations, thus prolonging a delay in cell selection and cell residence and decreasing the user experience.